Cell lines that are unable to fucosylate proteins are known in the art. A number of loss-of-function mutants that are unable to fucosylate proteins are known, perhaps most notably certain Chinese hamster ovary (CHO) cell mutants selected for resistance to certain lectins. Such cell lines are isolated by repeated selection for the inability to bind a particular lectin, e.g., the Lens culinaris lectin, in the presence of a mutagen. Other cell lines reportedly incapable of fucosylating proteins, e.g., antibodies, are known, see, e.g., U.S. Pat. No. 7,425,466 and U.S. Pat. No. 7,214,775 (α1,6-fucosyltransferase, i.e., FUT8 mutant). There remains a need in the art for cell lines with reduced ability to fucosylate proteins, in particular for cells with reduced fucosylation ability in the absence of a knockout, and for cells that conditionally fucosylate proteins.